1. Field of the Invention
This invention relates to a hydraulic device for hydraulic consumers for use in a production machine, particularly in an injection molding machine for processing synthetic materials or comparable plastic or plasticizable masses, comprising at least one control valve with at least three control positions; the control valve being regulable by at least one transducing means associated to a supply line by comparison of actual values with preset nominal values programmable in a control unit, whereby a variable capacity pump feeds consumers with fluid via the supply line leading over the control valve. The hydraulic device furthermore comprising a back flow pipe and a feedback line connecting a controlling device of the variable capacity pump with the supply line downstream of the control valve with the purpose of adjusting the pump output so as to maintain a constant operational pressure gradient.
2. Description of the Prior Art
A hydraulic device of this kind is disclosed in German Patent 31 19 095. In this device, the energy consumption of the variable capacity pump is adapted to a lower limit of the respective power requirements, by choosing as a basis for the operation and the control a just sufficient constant operational pressure gradient, presettable at the controlling device of the variable capacity pump. On the other hand, the known control device is adaptable to extremely different operational conditions, since a quantity, or pressure adjustment, diverging from the nominal value preset of the control valve is feedbackable alternatively by pressure transducers, distance detectors or distance potential transformers to the nominal value in the control circuit. However, such an appliance only can influence the influx side of the consumer.
A further hydraulic device is known from U.S. Pat. No. 4,823,551. In this device the supply lines are alternatively in connection with a common feedback line by means of a shuttle valve. The branch supply line, having an inferior pressure, is provided with a controller for fully stabilizing a nominal value deviation of the feeding current conditioned by a pressure asymmetry. Certainly, this method of simultaneously supplying several hydraulic consumers by the variable capacity pump is possible, however, only the influx side of the consumers is influenceable.
U.S. Pat. No. 5,129,806 discloses a hydraulic device for a consumer provided with a 4/4-way valve which is adapted to effect a differential switching, making it possible to feed the pressure line with fluid ousted by the consumer via a derived circuit provided with a nonreturn valve. In fact, the discharge of the fluid can be effected by an overlying pressure regulation, however, the expenditure involved is considerable, since a separate control valve has to be associated to each consumer.